Final Project: Phase Coding to Mitigate RangeVelocity Ambiguities

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Final Project Phase Coding to Mitigate
Range/Velocity Ambiguities

• Group 2
• Svetlana Bachmann, Aditya Turlapati
• May 2, 2005

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Outline

• Problem and its importance
• SZ(8/64) coding technique
• Simulation
• Algorithm
• Data
• Results
• Comparison
• Conclusions

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Problem and its importance

• Measuring of ra and va ? is limited due to rava
  c?/8.

Tradeoff ? measure long ra or large va
va , ra
va , ra
long Ts
short Ts
r-v ambiguities ? errors in the weather
observation
There are no solutions that can eradicate
completely the r-v ambiguities of weather echoes.
Phase coding is one of the techniques that can
help to mitigate the ambiguities.
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SZ(8/64) coding illustartion
ak(m)
ak(m 1)
V(m) V1(m) V2(m)

• ak exp( j?k)

V(m) V1(m) ak(m) V2(m) ak(m 1)
Ts
Cohering for the 2nd trip
( ) ak(m 1)
S(f)
V1(m) ak(m) ak(m 1) V2(m)
S1(f) S(f) S2(f)
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SZ(8/64) coding illustartion
ak(m)
ak(m 1)
V(m) V1(m) V2(m)

• ak exp( j?k)

V(m) V1(m) ak(m) V2(m) ak(m 1)
Ts
Cohering for the 1st trip
( ) ak(m)
S(f)
V1(m) V2(m) ak(m 1) ak(m)
S1(f) S2(f) S(f)
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SZ(8/64) coding illustartion
ak(m)
ak(m 1)
V(m) V1(m) V2(m)

• ak exp( j?k)

V(m) V1(m) ak(m) V2(m) ak(m 1)
Ts
Cohering for the 1st trip
( ) ak(m)
S(f)
V1(m) V2(m) ak(m 1) ak(m)
S1(f) S2(f) S(f)
Recovering weaker trip
Notch ¾ sc
( )ak(m 1) ak(m)
Cohering for the weaker trip
V2(m) S2(f)
S(f)
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Simulation Results an example
V weatherlike(S, v, ?v, M, va, SNR) V1
weatherlike(10, 15, 1, 64, va, 40)
(1) Generate 1st trip echo voltage V1. (2)
Generate 2nd trip echo V2. (3) Generate SZ code
ak (4) Encode both with proper phases (5) Sum
encoded voltages to create overlaid return
V2 weatherlike(5, -15, 2, 64, va, 40)
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Simulation Results an example
V weatherlike(S, v, ?v, M, va, SNR) V1
weatherlike(10, 15, 1, 64, va, 40)
(1) Generate 1st trip echo voltage V1. (2)
Generate 2nd trip echo V2. (3) Generate SZ code
ak (4) Encode both with proper phases (5) Sum
encoded voltages to create overlaid return
V2 weatherlike(5, -15, 2, 64, va, 40)
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Simulation Results SD(v2)
Ts 1.166 ms f 2705 MHz
ra 175 km va 23.8 m/s
v1, v2 are random (-va va)
P1 gtgt P2
w1 ?
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Simplified and Simplified Algorithm
Block diagram
Torres, S., D. Zrnic, and Y. Dubel, 2003 Signal
Design and Processing Techniques for WSR-88D
Ambiguity Resolution NOAA/NSSL Report, Part 7,
103 pp.
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Simplified and Simplified Algorithm

• Order weather
• Obtain time series data
• Estimate echoes location
• Cohere 1st trip signal
• Filter the ground clutter
• Cohere 2nd trip signal
• Estimate S, v, w to determine Stronger signal.
• Notch ¾ sc centered on the v of the Strong trip
  signal.
• Make the Weak trip signal coherent.
• Determine R and estimate v.
• Assign to a proper range
• Censor

2nd trip
long PRT
long PRT
1st trip
1st trip
???
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Data
10/08/2002 at 151103 UTC, elevation 0.5, f
2705 MHz

• ra cTs / 2
• va ? / 4Ts

Ts 1166 ?s ra 175 km va 23.8 m s1
Ts 3106 ?s ra 466 km va 8.9 m s1
175 km
466 km
350 km
Surveillance Scan
Doppler
SZ(8/64) Phase Coding
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Surveillance Scan
Large region of stratiform precipitation
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Surveillance Scan Th, r 350 km
Z, dB
Th
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Doppler Velocity, r 175 km
v, m s1
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Doppler Velocity, r 175 km, Th
v, m s1
Th
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SZ Doppler Velocity, r 350 km, Th
v, m s1
Th
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Ground Clutter example radial _at_ azimuth 297o
va 0 -va
va 0 -va
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Comparing SZ coding with no coding
http//cimms.ou.edu/rvamb/SZ/SZ_10_08_2002/
v, m s1
Z, dB
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Conclusions

• Phase coding allows
• to mitigate the r, v ambiguities
• significantly decrease the obscured area due to
  the overlaid echoes
• Phase coding fails
• in the regions where the strong GC overlays the
  second trip echo.